Transluscent leaf using principled shader
Final result:



I will show you two methods, first one (Translucent) is recommended because it's a lot faster approach and also with less geometry. For both of them you will need Mix Shader with Transparent BSDF and Alpha from Image Texture as a Factor.

Example above is rendered with only 32 samples. Beneath both meshes there is a light source to show the effect.

Translucent:



Simple mix between Principled BSDF and Translucent BSDF, both with Image Texture as a Color. Factor between them will allow you to control how much light will go trough mesh.

Subsurface:

For this method to work you will need to add some thickness to your mesh. I've added Solidify Modifier with pretty low value:



And node setup:



Choose color of Subsurface to be close to the Image Texture and set Subsurface strength.